As transmission capacities and rates of telecommunications network backbones constantly increase, fiber optic communication becomes a main transmission means of a modern information network. A photonic integrated circuit (PIC) chip is an important optical switching module. Because a cross section of an optical fiber is not strictly circular and the optical fiber may be affected by another factor such as a stress, polarization states of optical signals that enter the PIC chip from the optical fiber are uncertain. When these optical signals whose polarization states are uncertain directly pass through the PIC chip, an unignorable polarization dependent loss (PDL) and polarization mode dispersion (PMD) are caused, thereby reducing a signal-to-noise ratio of a system. Currently, to ensure transmission quality of a signal and eliminate impact of polarization, the PIC chip needs to separately process optical signals in different polarization states, where by using a technology such as a polarizer, a transverse electric wave (TE) mode and a transverse magnetic wave (TM) mode in the chip are separated into two optical paths for separate processing. A waveguide polarizer is an indispensable component of the PIC chip. Based on a principle that the TE mode and the TM mode have different propagation constants, different cut-off wavelengths, different coupling lengths, or the like, the waveguide polarizer allows only an optical signal in one polarization state (TE mode or TM mode) to pass through and blocks propagation of an optical signal in the other polarization state or absorbs an optical signal in the other polarization state.
In short, an existing waveguide polarizer generally can only produce polarized light in a fixed direction, that is, once designed and processed, the waveguide polarizer can only implement a polarization function of the TE mode or the TM mode. If optical signals in different polarization states are required, the only method is to first split original optical signals, and then install a polarizer for a required polarization state on each optical path. An implementation system is complex.